Apparatus for making sheet glass



May 26, 1964 B. LONG 3,134,660

APPARATUS FOR MAKING SHEET GLASS Filed 001;. 27, 1960 2 Sheets-Sheet lI7 IOGrophire 'Bernard Long INVENTOR.

AGENT- May 26, 1964 Filed Oct. 27. 1960 B. I oNc;` 3,134,660 APPARATUSFOR MAKING SHEET GLAss 2 Sheets-Sheet 2 FIGA FIG.5

-25 Platinum Alloy Berna rd Long INVENTOR.

United States, Patent 3,134,660 APPARATUS FOR MAKING SHEET GLASS BernardLong, Paris, France, assigner to GJM). Societe Anonyme Holding,Luxembourg, a corporation Filed Oct. 27, 1960, Ser. No. 65,533v Claimspriority, application France Oct. 30, 1959 3 Claims. (Cl. 65-157) Mypresent invention relates to an apparatus for producing sheets or stripsof flat glass by drawing a vitreous material from a molten bath.

In my co-pending application Ser. No. 793,442, tiled February 16, 1959,now Patent No. 3,000,142, issued September 19, 1961, of which thepresent application is a continuation-in-part, I have disclosed aprocess for producing sheet glass whereby a molten mass of vitreousmaterial entens a drawing chamber and is cooled therein in a controlledmanner so as to produce a first viscous skin on the upper surface of thebath and a second viscous skin on the lower surface of the melt incontact with the floor of the drawing chamber. The two viscous skins,upon cooling, give rise to a pair of relatively tough membranes orlayers between which a quantity of liquid glass is sandwiched as thesheets are drawn. The most effective membrane-forming process wasdescribed as one in which the upper and lower surfaces of the melt werecooled at'such a rate that the temperature gradients of the surfaceslalong the chamber were substantially equal and in excess of 100 C. perlinear meter. The formation of a lower viscous layer was shown toaccelerate the production of sheet glass by creating a pair ofparallel-moving films between which an entrained vitreous mass ofgreater fluidity could be withdrawn at high speed without causingsurface irregularities in the finished sheet.

In my co-pending application Ser. No. 12,635, filed March 3, 1960, Idisclose a method of and apparatus for further accelerating theproduction of sheet glass. In the latter application, the oor of thedrawing chamber is shown to be provided with an anti-fricton layer ofmolten metal adapted to reduce the frictional resistance between theglass flow and its support.

It is the principal object of my present invention t provide anapparatus for drawing flat glass, as generally disclosed in myabove-mentioned co-pending applications, adapted still further to reducethe frictional resistance between the molten vitreous mass and thedrawing chamber to accelerate production.

Another object of the present invention is to provide means for reducingthe frictional resistance along the lateral retaining walls of thedrawing chamber as well as along the iloor thereof.

According to a feature of the invention, the refractory wall surfaces ofthe feeding trough and the drawing chamber of an apparatus for makingflat glass are provided with a lining of a material whose coeicient offriction is substantially less than that of the refractory walls andwhich is not wettable or only slightly wettable by molten glass. Thelayer should consist of substances incapable of reacting with thevitreous mass even at elevated temperatures, i.e. under the conditionsprevalent in the drawing chamber, so as not to modify the composition ofthe glass. The friction-reducing layer may line the lateral retainingand end walls of the chamber as well as the floor thereof.

As these terms are used in the present disclosure, a globule of liquidglass does not wet a solid surface contacting this globule when theangle of contact is greater than 90 measured on the side where the glasscontacts the solid surface. If this angle is slightly less than 90, thesolid surface is only slightly wetted by the glass. Both of theseconditions are encompassed by the term substantially non-wettable.

The anti-friction lining may comprise a graphitic layer covering theglass-retaining walls and the floor of the Y drawing chamber, which isnot wetted by liquid glass. The graphitic lining, preferably in the formof relatively inexpensive and readily manufactured slabs, eifectivelyreduces the frictional resistance to the displacement of liquid glassand of the solidifying glass membranes at the upper and lower surfacesof the vitreous bath through the drawing chamber. I have found that thismaterial will not react objectionably with the vitreous mass, and willnot give rise to gases capable of altering the physical characteristicsor the coloration thereof, if the impurity level of the graphite slabsis carefully controlled. Accordingly, the slabs should not containimpurities in excess of 0.3% by weight, while specifically thequantities of titanium oxide and iron oxide should be less than 0.05%.Graphite slabs of such high purity are currently available commercially.

These slabs have been found to be substantially nonreactive at thetemperatures prevalent along the floor of the drawing chamber, which isgenerally cooled to maintain a temperature in the vicinity of 900 C., aswell as along the uncooled lateral walls where the temperature may rangeup to ll00 C.

According to a more specific feature of the invention, the graphitelayer'is not permitted to come into contact with the oxygen-containingambient atmosphere in order to prevent oxidation and, consequently,deterioration of the slabs. The slabs may, for example, be fullysubmerged below the level of the liquid glass to a depth so slight thatthe top layer of the liquid glass, which thus contacts-directly therefractory blocks of the dischagechamber structure above and behind thegraphite slabs, will experience only a minor increase in frictionalresistance. For a maximum reduction of the frictional resistance, thelevel of the liquid glass in the chamber is maintained somewhat belowthe tops of the slabs lining the lateral walls thereof to eliminate alldirect contact between the lateral surfaces of the melt and therefractory chamber walls. The free or exposed surfaces of the slabs arethen bathed in an oxygen-free atmosphere (c g. nitrogen or carbondioxide) to minimize the possibility of atmospheric oxidation of theslabs.

The need for a protective atmosphere can be avoided if the graphite isreplaced by a non-carbonaceous frictionreducing layer consisting, forexample, of a ceramic rnixture composed mainly of vanadium oxide (V205)and aluminum oxide (A1202). A particularly suitable ceramicanti-friction layer comprises the ceramic mixture marketed under thetrade name Vanal which contains 34% A1203 and 64% V205. The layer may beapplied to the refractory blocks constituting the inner surface of thedrawing chamber as a coating of suiiicient thickness to prevent contactbetween the liquid glass andthe refractory blocks, or may be cast ormolded to form slabs, similar in form to those of graphite previouslydescribed, and then positioned along the interior walls of the chamber.Under the temperature conditions generally maintained in the chamber,there is small risk of incorporation of traces of vanadium oxide in theglass melt so that no noticeable change of coloration occurs. i

Another substantially inert anti-friction liner according to myinvention may be a surface foil of a noble metal or alloy which does notadhere to glass under the temperature conditions of the drawing chamber.Platinum, for example, alloyed with one or more precious metals, e.g.Platinum Il, marketed by Degussa Hanau, is particularly suitable forlining the glass-contacting surfaces of a drawing chamber.

The above and other objects, features and advantages of my inventionwill become more readily apparent from the following description,reference being made to the accompanying drawing in which:

FIG. 1 is a longitudinal cross-sectional View of a sheet- .3glass-drawing chamber according to the present invention;

FIG. 2 is a cross-sectional view taken along line II--II of FIG. 1;

FIG. 3 is a view similar to FIG. l illustrating a drawing chamberprovided with a frieten-reducing lining along its terminal wall; and

FIGS. 4, 5 and 6 are views similar to FIG. 3 but showing otherterminal-wall linings.

In FIGS. 1 and 2 I show a feeding trough 4 which sup'- plies a drawingchamber 5 with a stream of liquid glass l from the interior of a tankfurnace (not shown), as generally described in my aforementionedco-pending applications. The liquid glass 1 continuously moves in thedirection of arrow la to feed the sheet 2 which is continuously drawnfrom the melt at the drawing chamber 5 over a roller 20 and betweenconventional cooling boxes 30.

The feeding trough 4 and the drawing chamber 5 are formed fromcontiguous bottom blocks 8, lateral blocks 11 positioned along thelongitudinal sides of the chamber, and a terminal wall 6 which extendstransversely to the longitudinal blocks 11 at the end of the drawingcharnber to form a draw pot. The blocks are all of refractory materialto withstand the high temperatures of the glass melt. The side blocks 11abut outer walls 16 made of a thermally insulating material. The floorof feeding trough 4 and drawing chamber 5, formed by the blocks `8 whichare preferably less than cm. thick to facilitate heat transfer from themelt 1, are cooled by a spray of coolant from pipes against theundersurfaces 7 and 9 of the feeding trough and the drawing chamber,respectively.

The interior surfaces of the blocks 8 and l1 are provided with anon-wettable layer in the form of graphite slabs 10 and 12,respectively, to which the liquid glass 1 does not adhere and whichreduces frictonal resistance to the ilow of the liquid glass in thedirection of arrow 1a and to the displacement (arrow 17a) of the lowervitreous membrane 17 formed at the cooled floor of the trough and thechamber. The lateral graphite slabs 12 are disposed so that their upperextremities 14 are below the upper surface 3 of the glass in order toprevent oxidation and deterioration of the graphite. To prevent liquidglass from entering the interstice between the slabs 12 and the lateralblocks 11, I prefer to cover the upper edges 14 of the graphite slabs 12with beveled blocks 113 of refractory material. The surface tension ofthe liquid glass in contact with the beveled portion of the blocks 13prevents the flow of glass behind the slabs 12. Since the graphite slabs12 are not wetted by the liquid glass, there is a substantial reductionin the frictional resistance to the stream of glass I along the lateralwalls of the feeding trough 4 and the drawing chamber 5.

In FIG. 3 I show a drawing chamber similar to that illustrated in FIGS.1 and 2 wherein, however, the terminal wall 6, which the lower glassmembrane I7 contacts as it is drawn upward to form the distal layer ofthe developing sheet 2, is provided on its inner surface 18 with afrieten-reducing layer constituted by graphite slabs 12a. The slabs 12aare covered by a refractory block 13a, as described with reference toslabs 12 and blocks 13, to prevent the ow of glass behind the slabs 12a.The beveled surface 21 of block 13a engages the rising glass membrane 17to prevent exposure of the slabs 12a to atmospheric oxygen.

FIG. 4 shows a drawing chamber and a feeding trough, similar to thosepreviously described, wherein the slabs 12 and 12:1 extend above thesurface of the liquid glass 1 and the protective blocks I3 and 13a havebeen dispensed with. A plurality of pipes 22 and 22a, preferably ofinert and refractory material (e.g. hardened porcelain or siliconcarbide), are arranged about the perimeter of the bath for the admissionof a pre-heated non-oxidizing gas (eg. nitrogen) which blankets theexposed portions of graphite slabs 12 and 12a to prevent oxidationthereof. The heated gas streams are advantageously directed against theinner walls of the trough and the chamber.

The linings 12a of the terminal wall 6 of the draw pot (FIGS. 3 and 4)have been replaced in FIG. 5 with a graphite block 23 shaped to divertthe lower membrane 17 of glass gradually upwardly where it joins thesurface membrane 3 at 19 to form the sheet 2. The bends of almost of thelower membrane 17 as the latter rises abruptly at the terminal wall 6,as illustrated in FIGS. l, 3 and 4, may produce undulations in thesurface of sheet 2 formed by membrane 17 which are obviated when themembrane is diverted upwardly in a gradual manner as shown in FIG. 5.

In FIG. 6 I show the blocks 6, 8 and 11 of the masonry constituting thechamber structure provided with an inner lining 25 of a platinum-alloyfoil which is not wetted by the liquid glass 1. It will be noted thatthe protective blocks 13, 13a (FIGS. 1-3) and the protective atmosphereintroduced via pipes 22, 22a (FIGS. 4 and 5) are not necessary in viewof the non-oxidizing and inert character of the foil.

I claim:

1. In an apparatus for the production of at glass including an elongatedhorizontal trough of refractory material forming an upwardly openchannel of constant depth for the ow of molten glass, said channelhaving a terminal portion provided with means for drawing a glass sheetin upward direction from two relatively viscous vitreous membranesrespectively formed at the top and at the bottom of the channel, thecombination therewith of a graphite layer covering the floor of saidtrough, and cooling means underneath said trough for directing a coolingfluid against the underside of said floor, thereby promoting theformation of the lower one of said membranes in a stratum of said flowdirectly above said graphite layer.

2. The combination defined in claim 1 wherein said trough has lateralwalls lined internally with further graphite layers up to a level nearthe top of said channel.

3. T he combination defined in claim 1, further comprising supply meansnear the top of said trough for admitting a nonoxidizing gas to saidchannel above the ow level.

References Cited in the le of this patent UNITED STATES PATENTS1,453,842 Jacobs May 1, 1923 1,469,383 Crowley Oct. 2, 1923 1,489,823Crowley Apr. 8, 1924 1,670,167 Reece May 15, 1928 1,818,205 Drake Aug.11, 1931 1,872,699 Drake Aug. 23, 1932 2,777,254 Siefert et al Jan. 15,1957 2,911,759 Pilkington et al. Nov. l0, 1959 FOREIGN PATENTS 635,934France Jan. 3, 1928 782,149 Great Britain Sept. 4, 1957

1. IN AN APPARATUS FOR THE PRODUCTION OF FLAT GLASS INCLUDING ANELONGATED HORIZONTAL TROUGN OF REFRACTORY MATERIAL FORMING AN UPWARDLYOPEN CHANNEL OF CONSTANT DEPTH FOR THE FLOW OF MOLTEN GLASS, SAIDCHANNEL HAVING A TERMINAL PORTION PROVIDED WITH MEANS FOR DRAWING AGLASS SHEET IN UPWARD DIRECTION FROM TWO RELATIVELY VISCOUS VITREOUSMEMBRANES RESPECTIVELY FORMED AT THE TOP AND AT THE BOTTOM OF THECHANNEL, THE COMBINATION THEREWITH OF A GRAPHITE LAYER COVERING THEFLOOR OF SAID TROUGH, AND COOLING MEANS UNDERNEATH SAID TROUGH FORDIRECTING A COOLING FLUID AGAINST THE UNDERSIDE OF SAID FLOOR, THEREBYPROMOTING THE FORMATION OF THE LOWER ONE OF SAID MEMBRANES IN A STRATUMOF SAID FLOW DIRECTLY ABOVE SAID GRAPHITE LAYER.